Various applications exist where substances, being in the solid phase when under ambient conditions, must be melted in order to be used, or where such substances must be transported in a molten condition. This scenario is for instance encountered when working with bitumen. Bitumen is a viscous substance that is typically used for road surfacing, waterproofing (for instance in tunnels and dams) or roofing. The bitumen must be applied in the liquid phase, i.e. a molten condition, and is then allowed to coagulate once applied. It will be appreciated that it will be advantageous to keep the bitumen in a molten state until used, and also to be able to melt the bitumen in a/solid phase within a reasonable time period.
Problems which are associated with conventional bitumen heating systems are well recognised and can be summarized as follows:    (i) During re-heating of a bitumen-type product with conventional systems, the product is subjected to thermal shock and can become severely degraded. Such degraded bitumen becomes unsuitable for road and pavement surfaces and results in early deterioration, as the thermal shock results in formation at micro fissures in such surfaces due to the change of the ductility of the bitumen.    (ii) As mentioned above, because bitumen is a poor conductor of heat, a considerable period of time is required to re-heat the bitumen. With conventional systems, such period is typically in excess of 20 hours per container. The long heating period which is required with conventional systems is also to a large degree attributable to the inefficiency of such systems.    (iii) Because of the long heating period described in (ii) above, a considerable amount of energy in the form of heating fuel is required to bring the bitumen to the required temperature. Such fuel costs can form a significant part of the cost of civil construction.